FFT Lib?

[dsimcha]

== Quote from Don (nospam at nospam.com)'s article
> dsimcha wrote:
> > I'm going to need an FFT library to perform some convolutions at some point
> > soon.  Two absolute, non-negotiable requirements are that it be written in
> > pure D and that it be Boost or compatibly (i.e. zlib or public domain)
> > licensed.  I also prefer "simple and good enough"
> What does "simple" mean?
> If you're happy with lengths being restricted to powers of 2, it's
> simple. Most of the complexity of something like FFTW comes from support
> for arbitrary lengths.

Yeh, I only need powers of two.  I realize this isn't very hard because I wrote a
prototype of it a while back.  However, this prototype would basically need to be
rewritten b/c:

1.  It only supports pure real inputs, meaning you can't use it to compute inverse
FFTs.

2.  I tried to write it using strides instead of rearranging the elements of the
arrays, mostly because I was curious what effect this would have on performance.
It turned out to be disastrous, presumably because it killed cache efficiency.